/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.solr.search.function;

import java.io.IOException;
import java.util.Map;
import java.util.Objects;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.queries.function.FunctionValues;
import org.apache.lucene.queries.function.ValueSource;
import org.apache.lucene.queries.function.docvalues.DoubleDocValues;
import org.apache.lucene.queries.function.valuesource.MultiFunction;
import org.apache.lucene.search.IndexSearcher;

/**
 * Abstract {@link ValueSource} implementation which wraps two ValueSources and applies an
 * extendible double function to their values.
 */
public abstract class DualDoubleFunction extends ValueSource {
  protected final ValueSource a;
  protected final ValueSource b;

  /**
   * @param a the base.
   * @param b the exponent.
   */
  public DualDoubleFunction(ValueSource a, ValueSource b) {
    this.a = a;
    this.b = b;
  }

  protected abstract String name();

  protected abstract double func(int doc, FunctionValues aVals, FunctionValues bVals)
      throws IOException;

  @Override
  public String description() {
    return name() + "(" + a.description() + "," + b.description() + ")";
  }

  @Override
  public FunctionValues getValues(Map<Object, Object> context, LeafReaderContext readerContext)
      throws IOException {
    final FunctionValues aVals = a.getValues(context, readerContext);
    final FunctionValues bVals = b.getValues(context, readerContext);
    return new DoubleDocValues(this) {
      @Override
      public double doubleVal(int doc) throws IOException {
        return func(doc, aVals, bVals);
      }

      /**
       * True if and only if <em>all</em> of the wrapped {@link FunctionValues} <code>exists</code>
       * for the specified doc
       */
      @Override
      public boolean exists(int doc) throws IOException {
        return MultiFunction.allExists(doc, aVals, bVals);
      }

      @Override
      public String toString(int doc) throws IOException {
        return name() + '(' + aVals.toString(doc) + ',' + bVals.toString(doc) + ')';
      }
    };
  }

  @Override
  public void createWeight(Map<Object, Object> context, IndexSearcher searcher) throws IOException {
    a.createWeight(context, searcher);
    b.createWeight(context, searcher);
  }

  @Override
  public int hashCode() {
    int h = a.hashCode();
    h ^= (h << 13) | (h >>> 20);
    h += b.hashCode();
    h ^= (h << 23) | (h >>> 10);
    h += name().hashCode();
    return h;
  }

  @Override
  public boolean equals(Object o) {
    if (!(o instanceof DualDoubleFunction other)) return false;
    return Objects.equals(this.a, other.a) && Objects.equals(this.b, other.b);
  }
}
